Potential benefits of exogenous neurotransmitters in alleviating transport stress in koi carp, Cyprinus carpio

The transport of live fish is an important process in the ornamental fish trade. As such, reducing transport stress plays a vital role in improving fish survival and minimizing economic losses. The objective of this study was to assess the efficacy of exogenous neurotransmitters in alleviating transport stress in koi carp, Cyprinus carpio. First, fish were subjected to simulated transport, and samples were collected at 0, 4, 6, 12, 24, and 48 h for the determination of water quality parameters and serum indices. The results indicated that the pH of the water decreased and ammonium nitrogen (NH4-N) was enhanced with the increase of transport time. The most significant changes in stress-related indices were observed at 4 h after transport, and thus the subsequent transport experiments were scheduled for 4 h. Three types of exogenous neurotransmitters were added to the water, and fish were transported for 4 h to determine the efficacy of the neurotransmitters. Gamma-aminobutyric acid (GABA) increased the pH, and decreased the NH4-N content of the water. The concentrations of serum adrenaline, cortisol, and glucose were decreased by GABA supplementation. Guanidine acetic acid (GAA) increased the pH of the water, and decreased the concentrations of serum adrenaline and cortisol. The addition of 5-hydroxytryptamine (5-HT) lowered the NH4-N level of the water, and decreased the concentrations of serum adrenaline and cortisol in the fish. In conclusion, the addition of exogenous neurotransmitters to transport water may help to alleviate transport stress by improving water quality and depressing the enhancement of stress-related hormones.